As for a film/fabric structure such as baseball parks, domes for various events, football stadiums, tent storages, gymnasiums, markets, and so forth, the materials used for sunshades of stores, truck hoods, mulching sheets, and so forth, the water-proof cloths used for raincoats, bags, chairs, and so forth, the materials of fiber-reinforced resins for belt conveyers, timing belts, and so forth, they are coated with transparent or colorless transparent surface coatings in order to maintain transparency and antifouling property. Here in this document a substrate refers to the above mentioned sheet products themselves or the materials used for these sheet products, and also to those coated with the surface coatings or to those before coated.
As for the known technology, a surface coating on the substrate is formed for improvement of the stability or the antifouling property, and as these coatings the transparent or colorless transparent surface coatings have been used in order to preserve the color or transparency of substrates made of film/fabric or fibers. As for the said coated materials, the fiber cloths woven from glass fiber or the like coated with fluorocarbon resin layer are known. These coated materials are water-repellent (the contact angle with water is 115-125°), and have such merits as incombustible, high mechanical strength, light-weighted, and flexible. However, the materials coated with fluorocarbon resin layer have faults that tend to collect dirt from the atmosphere such as smoke and soot, dusts, or fine yellow sands from the continental desert.
The photocatalysts of the late technology are coated on the surface of various materials such as a glass substrate. When an ultraviolet light in the sunshine is irradiated on the photocatalyst, organic contaminants on the surface of the material are decomposed by the redox reaction of the photocatalyst and this function is utilized for materials that need the so-called antifouling property. A binder containing the photocatalyst is used to coat the photocatalyst on a glass substrate. For example, U.S. Pat. No. 5,616,532 (reference 1) discloses the composition in which non-oxidizable polymer materials as the binder and titanium oxide fine particles are mixed in the solvent. The reference 1 discloses that the non-oxidizable polymer is such as silicone resins as the binder, and porous alumina and silica, colloidal tin oxide, or their mixtures are used. According to the reference 1, this binder is suggested to be coatable on the surface of such materials by drying or cure (low temperature treatment) as plastics or fibers which would otherwise requires thermal treatment (sintering) for coating, but the method to coat fluorocarbon resin layer containing the photocatalyst on the fluorocarbon resin layer is not suggested.
As for the method to coat fluorocarbon resin layer containing the photocatalyst on the substrate, Japanese Patent Application, JP 09-207289 A (reference 2) and JP 10-44346 A (reference 3) disclose the repeated coating of the dispersion containing titanium oxide fine particles as photocatalyst on the PTFE, fluorocarbon resin, layer, drying, and baking, and thus forming the PTFE layer on the surface of which are exposed the titanium oxide fine particles as the photocatalyst.
JP 11-47610 A (reference 4) and JP 11-47612 A (reference 5) disclose the forming of the photocatalyst layer by coating and baking of the dispersion containing PTFE powder and photocatalyst fine particles on the PTFE layer which is the reinforcing or supporting layer of film/fabric structure.
There is the problem that when the hydrophilicity was realized by introducing such ceramic components as aluminum fluoride into fluorocarbon resin, the hydrophobicity was gradually regained, thereby sufficient antifouling property could not be attained. And solving this problem, JP 09-76395 A (reference 6) disclose the fluorocarbon resin material of the fluorocarbon resin containing the photocatalyst coated on the flat and smooth surface of aluminum alloy substrate and the method to make hydrophilic the surface of fluorocarbon resin material, and suggests that the hydrophilicity defined as the contact angle with water below 90° was obtained.
In case that the surface area of the film/fabric structure is large, it is constructed by assembling many substrates for the structure. In this case it is required to weld each substrate in order to prevent leakage of water and air into the film/fabric structure. In the existing technology of the substrate that is coated with fluorocarbon resin, the thermal welding between the substrates for film/fabric structure by the hot welding the fluorocarbon resin tape of the same material and which is broader than the overlapped part. However, in case of the substrate the surface of which is coated with fluorocarbon resin, mutual thermal welding of substrates is possible, but its surface tends to be readily contaminated, and its cleaning cost tends to be high in case of large scale film/fabric structure such as outdoor stadiums.
On the other hand, in case of the photocatalyst sheet in which fluorocarbon resin layer contains photocatalyst, thermal welding is difficult for the fluorocarbon resin layer containing such inorganics as titanium oxide as photocatalyst and it is difficult to thermally lap-weld the photocatalyst sheet with large area. Hence the photocatalyst sheets with good thermal weldability and good antifouling property at welded parts are not so far materialized.
Also as disclosed in said reference 6, since the method to make hydrophilic the surface of fluorocarbon resin material on the flat and smooth aluminum alloy substrate is by the function of the photocatalyst irradiated with ultraviolet light, there are such problems as making sufficiently hydrophilic the material surface requires many days, contaminant accretes during the time, thereby sufficient antifouling property can not be attained by cleaning effect by making hydrophilic the surface region which was hydrophobic (contact angle about 90°) before the ultraviolet light (hereinafter the abbreviated term UV to be appropriately used) irradiation.